The invention relates to a system for supporting trays of seeded soil plugs during a period of greenhouse growth. More specifically, the invention is directed to a system for supporting trays with high-density arrays of seeded soil plugs in a greenhouse to insure proper initial growth of the plants before they are transplanted to the field.
In the transplant approach to crop cultivation the crops are started from seeds planted in soil plugs or soil masses, which are grown initially in greenhouses in a controlled environment. The greenhouse environment provides for an extremely high starting rate of the seeded soil masses. After the sprouted plants reach a certain level of maturity, they are transplanted to the field. Germination in the controlled environment of the greenhouse gives the plants a high probability of survival in the field.
U.S. Pat. Nos. 4,034,508 and 4,130,072, issued July 12, 1977, and Dec. 19, 1978, respectively, to Dedolph disclose a method of making an elastomeric soil plug, molded from a mixture including a soil compound such as peat moss, plant nutrients, and a biodegradable polymer resin binding the mixture together. In this technology transplant plugs can be formed with sufficiently small size and structural integrity to accomodate a single seed within an individual plug, and the seeded plugs can be carried by transplant trays in high-density arrays typically five-eighths inch on center. The seeds germinate and undergo their initial stages of growth under the controlled conditions of the greenhouse while in the trays, and the sprouted plugs are then transplanted from the trays to the field for further growth.
One of the advantages of the elastomeric soil plug technology is that it achieves a much greater uniformity in the harvested crop than has been attainable in the past. Although some variation in harvested crop will inevitably occur due to varying soil and weather conditions, the greater uniformity achieved with elastomeric soil plugs comes about because the entire process--fabricating and seeding the soil plugs, regulating the greenhouse environment in which the plants are nutured, and transplanting the sprouted plugs at controlled intervals and depths in the field--is amenable to automatic and highly regular machine handling. Uniformity of crop maturation time is, of course, highly desirable to minimize the amount of underripe or overripe crop harvested along with the bulk of properly ripened crop at harvest time.
In the greenhouses the trays are supported along their bottoms by elongate parallel rails, along which individual trays may be positioned to form long rows of abutting trays. During the greenhouse growing period even identically fabricated and seeded trays show a non-uniformity in the growth of seedlings in those plugs located along the supported sides of the trays. The rows of soil plugs at the support rails mature at a faster rate than those which are more removed from the rails, apparently due to different ambient environmental conditions, such as humidity and air circulation, in close proximity to the rails. Not only do the tops of the seedlings positioned along the support rails grow higher, but also the root systems of the seedlings grow beyond the soil plugs and through drain apertures in the bottoms of the trays into the interstices between the tray and support rails. Such seedlings develop differently in the field. In the first instance, they have a head start and consequently will mature and ripen at a faster rate once transplanted to the field. However, their overgrown root systems are more susceptible to damage during handling. Should the root system be damaged, the seedling will suffer root system shock and either mature at a lower rate or possibly die. Since the number of plugs along the supported edges of a tray amounts to roughly 10 percent of the total, the stimulated growth they experience can lead to significant variations in the crop at harvest time.